The present invention relates to an interlock system which prevents transmission shifting unless the clutch pedal is fully depressed.
A known manually operated synchronized transmission includes a pair of ratio selecting shift rails which are moved in order to shift the gear ratio of the transmission and a clutch pedal which is depressed to disengage a clutch. A pair of detent balls interact with the shift rails to prevent both rails from being moved simultaneously. However, with this transmission it is possible to move either rail and perform a gear or speed shift when the clutch is not fully disengaged. This can damage the synchronizers of the transmission.
A commercially available tractor includes a transmission with a pair of shift rails and a clutch interlock, but the interlock locks the position of only one of the shift rails and does not prevent all possible gear shifts when the clutch pedal is not fully depressed.
U.S. Pat. No. 4,146,120, issued in 1979 to Stevens discloses a transmission control system for a 6 speed transmission wherein a gated speed select lever is coupled to a single speed select spool and to a neutral select spool in a hydraulically actuated control unit. Different transmission speeds or gear ratios are selected by moving the speed select spool. A clutch control lever is coupled to a hydraulic control unit which controls a hydraulically operated input clutch. It appears that a hydraulically operated interlock detent mechanism prevents movement of the neutral select spool, which in turn prevents the speed select lever from moving out of its neutral position unless the clutch control lever is moved to disengage the clutch. This detent mechanism requires a complicated arrangement of hydraulic valves, conduits and actuators. This system does not have a pair of movable speed select spools.
It would be desirable to have a simple interlock mechanism for a transmission having at least a pair of speed select rails or spools and which prevents speed selecting through both rails unless a clutch pedal is fully depressed and the clutch is fully disengaged.
Accordingly, an object of this invention is to provide a system for a transmission with a pair of shift rails which prevents gear shifts via these shift rails unless the clutch is completely disengaged.
A further object of the invention is to provide such a system which does not require complex hydraulic valves and circuitry.
These and other objects are achieved by the present invention, wherein an interlock mechanism is provided for a transmission system. The transmission system includes a gear unit with a plurality of selectable gear ratios, a manually operated clutch control member or pedal manually movable from an engaged position to a disengaged position, and a pair of shift rails movable to select gear ratios. Each rail has a detent groove formed therein. The transmission also includes a pair of detent balls which operatively engage the shift rails. The interlock mechanism includes an interlock member which is movable from a lock position wherein the interlock member engages both balls and holds both of them partially received by the detent grooves in the rails, to a release position wherein the interlock member is spaced apart from both detent balls, and the balls interact with the grooves to permit one or the other of the rails to move.
The interlock member is non-rotatably mounted on a rotatable shaft and an interlock lever is non-rotatably coupled to the shaft. An interlock spring is coupled to the interlock lever and is biased to urge the interlock member to the lock position. A push/pull cable couples the lever to the clutch pedal so that when the clutch pedal is depressed to its clutch fully disengaged position, the lever pivots and moves the interlock member to move to its release position. The rails are supported by a pair of spaced apart rail support members. Each support member has a bore which slidably receives a corresponding one of the rails and has a notch or opening extending from the bore to a surface of the support member facing towards the other support member. Each detent ball is held in a corresponding one of the notches and adjacent a corresponding detent groove.
The interlock member, when in its lock position, is positioned between the support members and between the detent balls, and engages both detent balls and moving both detent balls into their corresponding detent grooves to prevent movement of both rails, the interlock member, when in its release position, being positioned apart from both detent balls to allow both detent balls to move out of their corresponding detent grooves to prevent movement of one of the rails.